The invention concerns devices of the type described in Patent EP-A-0 519 850 (TECHNIFOR). It will be recalled that, in these devices, the marking tool, of the micro-percussion type, is mounted axially at the end of a slewable rod of which the opposite end penetrates inside a fixed housing through an articulated link constituted equally well by a Universal joint and by a simple ball-joint.
In order to control orientation of the tool-holder rod, the housing contains an actuation mechanism which comprises two telescopic jacks oriented parallel to each other to act on two arms fixed radially on the rod and disposed perpendicularly to each other. One of the two elements of each jack is coupled by a ball-joint to the housing, while the other element is connected, itself by a ball-joint, to the end of the radial arm which corresponds thereto.
In one of the embodiments described in the prior art document mentioned hereinabove, the two actuation jacks are oriented parallel to the axis of symmetry of the slewable rod, being coupled to that wall of the housing opposite the one which bears the articulated link. It will be appreciated that, if this rod is retained angularly against any rotation along its axis, such an actuation mechanism ensurers control of the displacement of the tool under excellent conditions.
However, it should be noted that such an arrangement also presents a substantial drawback, in that, due to the geometry of the assembly, any control exerted by one of the two jacks necesarily involves a correcting action applied to the other jack, even in the case of the device being used for marking rectilinear lines. This permanent correction complicates the electronic apparatus used for controlling the actuation mechanism.
In order to overcome this drawback, Applicants have proposed, in their European Patent Application No. 94 420 041.9 filed on Feb. 9, 1994, disposing the ball-joints which ensure coupling of the telescopic jacks to the fixed housing, in the plane transverse to the slewable rod which passes through the centre of the articulated link interposed between this rod and said housing.
Such structure has proved to be of high performance, but it requires the use of jacks which are always very delicate to control very precisely. It is in this spirit that the present invention has for its object another embodiment which, by employing electric motors of the step-by-step type, makes it possible, at least in the case of the articulated link being constituted by a Universal joint, to simplify actuation of the device while maintaining the same performances.